Nonadiabatic Dynamics of Photoinduced Hydrogen Dissociation on Plasmonic Au Nanoparticles: How Hot Carrier Excitation Leads to Bond Breaking.

Abstract

Plasmonic nanoparticles have generated great attention due to their potential applications in photocatalysis. The dissociation of hydrogen on Au nanoparticles has served as a useful model for this process, but despite many previous studies, there are important details of the dynamics which remain uncertain, such how single-photon absorption triggers dissociation. This paper addresses these issues through the study of gold clusters interacting with H₂, explicitly examining the effects of cluster size, shape, and excitation energy on the dissociation dynamics. By using time-dependent density functional theory (TDDFT) interfaced with trajectory surface hopping, we have examined the Au + H₂ system for states with excitation energies similar to the plasmon energy in gold. Three distinct outcomes are observed: H-H bond dissociation, H₂ desorption, and nonreactive relaxation. Trajectories starting in excited states of the cluster relax through extensive nonadiabatic surface hopping to lower excited states that couple to antibonding states where repulsion drives dissociation. In addition, hopping converts metal excitation to increased kinetic energy in H-H stretching that helps overcome dissociation barriers on reactive adiabats. This provides a detailed picture of the evolution of hot carriers into antibonding states of physisorbed molecules after extensive surface hopping that dissociate in ∼100 fs. Desorption and nonreactive relaxation compete with this picture. Our findings provide insights to photoinduced processes involving plasmonic nanoparticles showing how nonadiabatic dynamics plays a crucial role in accessing repulsive states while also releasing kinetic energy that drives dissociation.